Synthetic natural gas or syngas comprises a gaseous mixture derived from carbon sources and contains chiefly hydrogen (H.sub.2) and carbon monoxide (CO) together with low amounts of other gases.
Synthetic gases of varying and controlled H.sub.2 /CO molar ratios are employed in various petrochemical processes, such as the production of methanol and oxo alcohols, aldehydes, acids, and other chemical compounds. One type of synthetic gas is produced by the reaction of steam and methane in a reformer, which reaction provides a synthesis gas, after carbon dioxide removal, of about a H.sub.2 /CO molar ratio of three (3) and a residual methane content of up to about five percent (5%).
It is desirable to produce a synthesis gas of a selected and lower H.sub.2 /CO molar ratio for use in particular petrochemical processes, such as a molar ratio of about 0.9 to 1.0 and also with a lower methane content.
U.S. Pat. No. 5,832,747, issued Nov. 10, 1998, hereby incorporated by reference, discloses a wholly cryogenic process for the cryogenic adjustment of the hydrogen and carbon monoxide molar ratio of a syngas, typically of even molar ratio. The process comprises partially condensing, in a cold box, at least a portion of the gaseous feed mixture and then separating the partially condensed feed mixture in a phase separator, to provide a gaseous product stream of a different H.sub.2 /CO molar ratio than the gaseous feed. The process includes warming the resultant product stream without any further cryogenic separation.
It is desirable to provide a new and improved process and system for providing from a syngas, a product gas of a defined selected H.sub.2 /CO molar ratio and a low methane content.